The present invention is a method for monitoring the condition of a highly resistive fluid(s) while in use in transportation or industrial equipment including but not limited to vehicles, machines, devices and the like. The invention has particular benefit for on-line monitoring and analysis of a diesel engine lubricant condition. More specifically, the invention has benefit in monitoring soot content of a diesel engine lubricant and in determining when the lubricant loses the ability to control the soot content for optimum engine performance and life.
Lubricating oil is critical to the life and performance of an internal combustion engine. When the lubricant has appropriate viscosity for the required hydrodynamic film, detergents and dispersants to suspend and/or neutralize undesired contaminants, and surface active chemicals to protect engine component surfaces, the lubricant allows for long, efficient engine operation by reducing friction, wear and corrosion of engine components. In general, a lubricant's performance characteristics change with use and age as the base oil and/or additives are consumed, degraded or depleted. A lubricant reaches the end of its useful life when any one of the lubricant's performance properties is outside a desired range. Using a lubricant past the end of its useful life reduces engine life and performance and possibly leads to catastrophic engine failure.
Lubricant value is maximized if used lubricant remains in an engine and is not replaced with fresh, i.e. unused, lubricant until the lubricant reaches the end of its useful life. However, due to the complexity of lubricant degradation, which can be a function of engine age, operating conditions and other factors, accurate determination of lubricant condition has traditionally required off-line laboratory tests which often are not cost and/or time effective for equipment operators. Hence, most operators simply estimate lubricant condition and change lubricant based on one or more easily measured engine operating parameters such as time of operation, mileage driven, fuel use or others, or they rely on algorithms by engine manufacturers that typically use one or more engine operating parameters, but no actual lubricant measurement. An issue with estimates or algorithms that use no lubricant condition measurement or specific information about the quality of the lubricant in the engine is that lubricant change decisions are made without knowing either actual condition or even potential useful life. Actual lubricant condition or potential life information is particularly important in lubricant change decisions for engines where contaminants such as soot play a major role in lubricant degradation since individual lubricants can vary widely in their ability to suspend and/or neutralize contaminants.
Recently sensors for real-time, on-board measurement of a lubricant's electrical, optical or other properties have been introduced; a good overview is given in “Determining Proper Oil and Filter Change Intervals: Can Onboard Automotive Sensors Help?”, Sabrin Khaled Gebarin and Jim Fitch, Practicing Oil Analysis, March-April 2004. Many of these sensors simply provide an output that is function of the measured lubricant property with no actual analysis of fluid condition. In general, sensors that do not provide a “fluid condition” output are of limited value to engine/equipment manufacturers who do not know the relationship, if any, between sensor signal and fluid condition. To overcome this limitation, some sensors attempt to provide a complete solution with hardware and/or software that interpret a fluid condition based on measured lubricant property. U.S. application Ser. No. 10/271,885, filed Oct. 16, 2002 entitled “Method for on-line monitoring of quality and condition of non-aqueous fluids”, Lvovich, et al. is a method for a relatively complete fluid condition analysis based a multitude of a fluid's electrical impedance responses. While the relatively complete fluid condition analysis is appropriate in some fluid applications, other applications require a more cost effective solution for interpretation of only a particular fluid condition; for example, diesel engine manufacturers and end-users have interest in monitoring soot related properties in the engine's lubricant. A lubricant's soot content, which is a consequence of the diesel engines' combustion process, provides information about the engine's operating condition, but more importantly, knowing if the lubricant is of appropriate condition to effectively maintain the soot in a stable suspension of finely dispersed particles is important to optimize oil change intervals.
US application 2004/0036487, entitled “Diesel engine lubricating oil contaminant sensor method”, to Heremans, et al. describes a sensor that attempts to meet the need for monitoring the soot content of the lubricant in a diesel engine. A limitation is that while the described sensor may measure lubricant soot content, the sensor does not determine if or when the lubricant begins to lose effectiveness in controlling the soot; that is, the point at which the additional soot content results in increased size of dispersed particles. A loss of a lubricant's ability to control soot, or more generally contaminants, is typically first identified by increased fluid viscosity, but typically occurs before a rapid viscosity increase is noted and, in any case leads, to reduced performance and service life of the engine.
Hence, there remains a need for an on-line fluid monitoring sensor to “real-time” determine not only of fluid contaminant, in particular soot, content but of when the fluid begins to lose its ability to suspend, disperse or otherwise control the contaminant in order that the fluid can be maintained to provide desired equipment performance and life.
Accordingly, the present invention provides a sensor with a method for on-line determining fluid condition based on a property that is consistent with contaminant content and when the fluid loses the capability of controlling contaminants while the fluid is in use in industrial or transportation applications.